The compounds of the invention can be prepared by methods analogous to those described by Pollak et al., Tetrahedron 22, 2073 (1966); and Bellasio et al., U.S. Pat. Nos. 3,915,968 and 4,016,162. Other methods are described in Miller and Rose, J. Chem. Soc. 1963, 5642: Basu and Rose, J. Chem. Soc. 1963, 5660 (1963); and Davies et al., Nature New Biology, 234 50 (1971).
The compound 3-morpholino-6-methyl-8-phenyl-s-triazolo[4,3-b]pyridazine was described by Yurugi et al., Takeda Kenkyusho 32 (2), 111-117 (1973). Other morpholino triazolopyridazines are described in French Pat. No. 1248409 and in Chemical Abstracts, 67 21884 g.